Currently available robot arm mechanisms include pivotally joined multiple linear links that are driven by a first motor and are mechanically coupled to effect straight line movement of an end effector or hand along radial directions from a central axis. Such robot arm mechanisms are also equipped with a second, independently operating motor to angularly displace the hand about the central axis. Certain robot arm mechanisms are equipped with telescoping mechanisms that move the hand also in a direction perpendicular to the plane of straight line movement and angular displacement of the hand. The hand is provided with a vacuum outlet that secures a specimen, such as a semiconductor wafer, computer hard disk, or compact disk, to the hand as it transports the specimen between processing stations.
U.S. Pat. No. 4,897,015 of Abbe et al. describes a rotary-to-linear motion robot arm that uses a first motor to control a multi-linkage robot arm to produce straight line radial motion from motor-driven rotary motion. An additional motor may be coupled to the robot arm for operation independent of that of the first motor to angularly move the multi-linkage robot arm without radial motion. Because they independently produce radial motion and angular motion, the first and second motors produce useful robot arm movement when either one of them is operating.
The robot arm of the Abbe et al. patent extends and retracts an end effector (or a hand) along a straight line path by means of a mechanism that pivotally couples in a fixed relationship a first arm (or forearm) and a second (or upper) arm so that they move in predetermined directions in response to rotation of the upper arm. To achieve angular displacement of the hand, a .THETA. drive motor rotates the entire robot arm structure. The Abbe et al. patent describes no capability of the robot arm to reach around corners or travel along any path other than a straight line or a circular segment defined by a fixed radius.
U.S. Pat. No. 5,007,784 of Genov et al. describes a robot arm with an end effector structure that has two oppositely extending hands, each of which is capable of picking up and transporting a specimen. The end effector structure has a central portion that is centrally pivotally mounted about the distal end of a second link or forearm. The extent of pivotal movement about all pivot axes is purposefully limited to prevent damage to vacuum pressure flexible conduits resulting from kinking or twisting caused by over-rotation in a single direction.
The coupling mechanism of a first link or upper arm, the forearm, and the end effector structure of the robot arm of the Genov et al. patent is more complex than that of the robot arm of the Abbe et al. patent. Nevertheless, the robot arm structures of the Abbe et al. and Genov et al. patents operate similarly in that each of the end effector structures picks up and transports specimens by using one motor to extend and retract a hand and another, different motor to rotate the entire robot arm structure to allow the hand to extend and retract at different ones of a restricted number of angular positions extending radially from a central axis.
Robot arms of the type described by the Abbe et al. and Genov et al. patents secure a specimen to the hand by means of vacuum pressure delivered to the hand through fluid conduits extending through the upper arm, forearm, and hand and around all of the pivot axes. The Abbe et al. patent is silent about a vacuum pressure delivery system, and the Genov et al. patent describes the use of flexible fluid conduits. The presence of flexible fluid conduits limits robot arm travel path planning because unidirectional robot arm link rotation about the pivot axes "winds up" the conduits and eventually causes them to break. Thus, conduit breakage prevention requirements prohibit continuous robot arm rotation about any of the pivot axes and necessitate rewind maneuvers and travel path "lockout" spaces as part of robot arm travel path planning. The consequences of such rewind maneuvers are more complex and limited travel path planning, reduced throughput resulting from rewind time, and reduced available work space because of the lockout spaces.
Moreover, subject to lockout space constraints, commercial embodiments of such robot arms have delivered specimens to and retrieve specimens from stations angularly positioned about paths defined only by radial distances from the axes of rotation of the robot arms. Thus, the robot arm structures described by the Abbe et al. and Genov et al. patents are incapable of transporting specimens between processing stations positioned in compact, irregularly shaped working spaces. For example, neither of these robot arm structures is set up to remove specimen wafers from and place specimen wafers in wafer cassettes having their openings positioned side-by-side in a straight line arrangement of a tightly packed working space.